On December 31, 2001, a land dispute in the Mambilla Plateau of
northeastern Nigeria turned violent. The U.N. Office for the Coordination of
Humanitarian Affairs reported that at least 40 people died, and hundreds were
displaced after fighting broke out between local farmers and nomadic herders.

Heavy rainfall enables the Kalahari sands to support lush rainforest (top), but substantially reduced rainfall in the south leads to sparser vegetation. Southern Botswana (bottom) is dry savanna. (Images courtesy of Hank Shugart, University of Virginia)

Data from the SAFARI 2000 project are archived at the Oak Ridge National Laboratory DAAC, which focuses on providing biogeochemical and ecological data for studying environmental processes.

Image in title graphic courtesy of Hank Shugart, University of Virginia

Who was at fault?

According to some analysts, the real culprit was desertification. The
conflict arose after a shortage of acceptable pasture pushed desperate herders
into farming regions.

French plant ecologist Andre Aubreville popularized the term
desertification in a 1949 paper. He wrote that the desert is always
present in the embryonic state during the dry and hot season. Sufficient
human pressure, Aubreville observed, can transform tropical rainforest into
savanna, and savanna into desert. Desertification now threatens more than a
billion people worldwide, although its impacts are most severe in Africa. A
major impediment to food production, degraded land means roughly $42 billion
each year in lost income. Outside the immediately affected areas, it can cause
flooding, reduce water quality, create dust storms, and increase incidences of
respiratory illness and eye infection.

But as serious as desertification is, its only part of the
problem. The phenomenon were concerned with is actually bigger, said
Dr. Hank Shugart of the Department of Environmental Sciences at the University
of Virginia. Were interested in land systems that can change from
something desirable to something undesirable, then stay that way.

Africas fragile ecosystems make the continent especially vulnerable
to unwanted environmental changes. Shugart compared Africa to parts of the
United States and Europe. In a place with rich soil, if you change the
ecosystem and you dont like the result, you can stop, and the system will
more or less restore itself. In parts of Africa and Australia, if you change the
land and start seeing results you dont like, you might get to look at them
for a long time.

Shugart developed an interest in large-scale ecosystems as a graduate
student. As a researcher in the Southern African Regional Science Initiative
(SAFARI 2000), he studies the big picture by looking at interactions between the
Earth, the atmosphere, and people. Shugart suspects that Africa supports two
kinds of savanna. One form produces palatable vegetation that the wildlife eats
and recycles locally, so the ecosystems nutrients (nitrogen and
phosphorus) remain in the system. The other form of savanna produces less
palatable vegetation; rather than being consumed by animals, this vegetation
accumulates, providing fuel for fires that transport nutrients somewhere
else.

If the low-nutrient ecosystems lose their nutrients, and the
high-nutrient systems keep theirs, are landscape processes robbing the poor to
give to the rich? Shugart asked. If so, this reinforces a serious problem.
Once an ecosystem thats easily grazed becomes an ecosystem thats
easily burned, it rarely reverts to its previous grazable state. Exactly how
ecosystems make this transition is not fully understood, but Shugart cites two
lines of evidence that fire-adapted ecosystems exist in places that could
support more benign vegetation: (1) previously forested regions have become
fire-prone savanna, and (2) high- and low-nutrient communities exist on similar
soils and under similar climatic conditions.

Sobering examples of unwanted ecosystem change can be found outside
Africa. Introduced plant species have substantially changed ecosystems in North
America. Cheatgrass burns like crazy, and its seeds can withstand fire. It
isnt good for anything else, so its been kind of a scourge in the
western United States, said Shugart.

Livestock grazing has also produced problems. When people first
encountered the Chihuahuan Desert in New Mexico, it probably had small shrubs
and aridity-tolerant grasses. Once cattle grazed it, everything turned to
creosote bush, which sends roots out 50 feet from the plant and sucks up all the
nutrients. So now the system is either high-nutrient with a bush growing on it
or low-nutrient desert. There are no nutrients between the bushes, so the
grasses cant come back  even if you stop the livestock
grazing.

A variety of natural grazers can keep an ecosystem in balance, but
livestock grazing has had far-reaching effects in Africas dry regions.
Africa has a beautiful assemblage of antelope, giraffes, and other big
animals that eat different kinds of plants, Shugart said. But cattle
are preferential grass eaters, so once they start grazing, the vegetation can
turn thorny and shrubby. Is that a reversible condition? Wed like to
know.

Ecosystems unlikely to recover from human pressures require more cautious
management. Making informed land-use decisions for such unforgiving ecosystems
means understanding the complicated relationship between environment and
vegetation. But such studies usually involve long time periods, making
controlled experiments difficult. The trick for Shugart and his fellow SAFARI
2000 researchers was to find natural experiments already in place. They found
what they wanted in the Kalahari Transect.

The Kalahari Transect extends from Angola and
Zambia south into South Africa. It is characterized by uniform sandy soils,
heterogeneous vegetation, and a strong rainfall gradient. Mean annual rainfall
varies from nearly 1.5 meters (5 feet) in the north to virtually no rain in the
south. (Image courtesy of Hank Shugart, University of Virginia)

In most places where vegetation changes over hundreds of miles, as
in the transition from the eastern forests to the Great Plains in the United
States, theres a change in climate, but theres almost always a
change in soil as well, Shugart said. The Kalahari has one type of
soil top to bottom  windblown sand. The rainfall changes in a very regular
way. These variables are naturally controlled along this thousand-mile
line.

Another controlling factor in the Kalahari Transect is land use. Much of
the area Shugart is studying is devoted to farming or game preserves, where the
land is essentially unused. Therefore, Shugart can compare the effects of fairly
basic differences in land use. Yet studying southern Africa has presented
Shugart with an uncommon problem. Ecologists want to see how an ecosystem
works naturally, and that usually means without people, he said, but
we evolved in southern Africa. The current land use patterns probably
didnt evolve there, but theres been a human presence for a few
million years. As humans have long known how to start fires, they have
augmented naturally occurring fires.

Scientists working with Christopher Justice at the
University of Maryland collaborated with Shugarts team to use MODIS imagery as the
basis for calculating fire emissions of carbon dioxide. The team calculated that
emissions from woodland fires totaled 180 Tg (teragrams, or a trillion grams),
and emissions from grassland fires totaled 52 Tg. (Image courtesy of Stefania
Korontzi and David Roy, University of Maryland Department of Geography)

Research conducted so far has already given Shugart valuable insights into
land-atmosphere interactions. Shugarts first expedition with SAFARI 2000
started in Zambia and headed south through the Kalahari Transect. Joined by
members of the Moderate-resolution Imaging Spectroradiometer (MODIS) land
validation team, he sampled vegetation intensively at six sites. Field Data from
the Kalahari Transect are available via the ORNL DAACs Mercury
system.

The MODIS sensor monitors, among other factors, aerosols and land surface
changes on the Earths surface every 24 to 48 hours. For fire emission
detection and vegetation mapping, Shugart uses MODIS imagery archived at
NASAs Land Processes DAAC. In addition to the standard size of 1,200 by
1,200 kilometers, the Oak Ridge National Laboratory DAAC has prepared 7- by
7-kilometer subsets of MODIS products over field investigation sites in southern
Africa. The subsets are used for validating individual MODIS pixel values
against measurements made in the field.

MODIS images vary between 500-meter and 1-kilometer resolution, so a
single pixel (the smallest visible unit in the image) actually represents a
large area. Five hundred square meters can easily contain a mix of grasses,
bushes, trees, and bare rock, yet the pixel can only record one type of ground
cover. The satellites going to average something out of the
picture, Shugart said. So he has supplemented MODIS data with
higher-resolution images and modeling techniques.

The SAFARI 2000 project obtained AirMISR imagery by flying the sensor on
an ER-2 aircraft over southern Africa during the study period. AirMISR data is
archived at Langley Research Center (LaRC). For historical data, Shugart relies
on newly declassified 2-meter resolution images taken by the CORONA spy
satellite between 1962 and 1972, now archived by the U.S. Geological Survey
(USGS). Were trying to make comparisons between satellite imagery,
aerial photos, and ground-truth data, said Shugart.

Shugart has also worked toward a model-based understanding of Kalahari
vegetation. A dozen bushes might display as the same shade of green in a
satellite image, regardless of their spatial distribution. Yet those bushes may
behave in very different ways depending on whether theyre clumped together
or separated by several meters. For this reason, SAFARI 2000 researchers have
begun making detailed models, known as stem maps, of fine-scale variations.
Refining these stem maps will be an ongoing process for Shugart and his
team.

Changes are obvious when comparing vegetation in
Lishuwa Village, Zambia (left) and Tshane, Botswana (right). At the top of the
transect, Lishuwa enjoys much greater rainfall. (Image courtesy of Hank Shugart,
University of Virginia)

As the study progresses, Shugart will examine fire models, burn scar
models, and emissions models to better understand what nutrients are lost to the
atmosphere across Africa. He is also involved in producing a special journal
issue of Global Change Biology devoted to SAFARI 2000 research.

Its easy to get isolated if youre a working scientist in
Africa, Shugart said. Africa doesnt have a huge number of
scientists yet, and the ones doing research are under a lot of pressure because
theyre in the middle of the problem. SAFARI 2000 has been a remarkable
project in that its arisen through grassroots coordination among
scientists. By working together, weve been able to pool our resources and
share information very quickly. It has been very refreshing.